Is it obligatory to call off a marriage to a girl who, along with her family, insists on holding a costly wedding ceremony that includes forbidden matters such as music and mixing?

What the girl's family desires—to hold a wedding that includes music and mixing (between genders)—is forbidden by Islamic law, and it is not permissible to agree to it. To resolve this situation, the following is recommended: Firstly, advise them kindly and explain the Islamic ruling, the prohibition of music and mixing, and clarify the possibility of holding a successful wedding without forbidden acts. Secondly, if that does not work, seek out wise individuals from their family or your family to intervene and pressure them to abandon the reprehensible acts. Thirdly, if that does not help, involve a scholar or a person of sound judgment to convince them. Fourthly, if they do not respond, threaten them with divorce and separation; perhaps they will pay attention. If they do not respond at all, then beware of getting involved with them, unless the girl is religious and of good character and does not approve of her family's actions, and both of you can avoid attending the forbidden acts and leave when they begin, while publicly denouncing and disassociating yourselves from them.